Happiness to make things darker? (7)

I believe the answer is:

delight

I'm a little stuck... Click here to teach me more about this clue!

'happiness' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for delight that I've seen before include "It could be Turkish" , "Ecstasy" , "Transport - please" , "charm" , "Jubilation" .)

I've seen this clue in The Sun.

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